The present invention relates to a stylet-free epidural catheter for insertion into a patient via a needle, as well as a thread assist device, both to reduce buckling of a catheter in and around the needle hub, and more particularly to a combination of such an epidural catheter and such a thread assist device.
Commonly assigned U.S. Pat. No. 5,947,940 entitled xe2x80x9cCatheter Reinforced to Prevent Lumenal Collapse and Tensile Failure Thereofxe2x80x9d is incorporated herein by reference. This patent discusses in detail the problems associated with medical catheters, and in particular an epidural catheter, and the need for reinforcement thereof to meet the rigorous requirements of an epidural catheter. The reinforcement disclosed is at least one helical reinforcing member (preferably predominantly non-metallic) wound around the longitudinal axis of the elongated tubular body of the catheter for reinforcing the body to prevent radial collapse thereof during bending and pinching thereof and to prevent longitudinal breakage thereof under tension. Such catheters have proven to be quite satisfactory in use and, in particular, as epidural catheters.
Nonetheless, the design of the catheter described above has proven to be less than totally satisfactory. Typically, the use of a stylet within the catheter is still required during the insertion operation. From the point of view of the catheter manufacturer, this results in additional costs, both for the manufacture of the stylet and for the insertion of the stylet through the catheter. From the point of view of the catheter user, an additional step in the procedure is required to ultimately withdraw the stylet from the catheter after the stylet has served its function of stiffening the catheter sufficiently to allow it to enter the epidural space (the ligamentum flavum). Due to the length of the stylet, this is a time-consuming and laborious operation step. Furthermore, the removed stylet is a contaminated xe2x80x9csharpxe2x80x9d which must be safely and specially disposed of in order to not expose room personnel to additional risks of contamination.
The prior art also teaches thread assist devices (TADs) which enter into the luer hub of the needle and preclude buckling (non-axial or lateral collapse) of the catheter just as the catheter distal tip is emerging from the distal end of the needle into the epidural space, a time when buckling tends to occur due to the additional resistance exerted by the ligaments of the epidural cavity. The known TADs preclude buckling of the catheter in the region of the needle hub by completely surrounding the catheter sidewall so that there is no room in which the catheter can buckle. On the other hand, this positioning of the TAD requires a practitioner to move the catheter forwardly through the needle from a point of contact (between the practitioner and the catheter) which is disposed proximally of the needle hub; this makes it more difficult for the surgeon to introduce a substantially straight or linear length of the catheter into the needle hub. At the very time that the practitioner is pressing on the catheter with his fingers and using friction (between his fingers and the catheter) to slide the catheter forwardly through the TAD and the needle, there is a tendency for the practitioner to laterally deflect the catheter before it enters the TAD so that it is no longer in axial alignment with the needle and the TAD. Thus, the need remains for a TAD for use with an epidural catheter (whether reinforced or not) which enables movement of the catheter slidingly along the needle without deflecting the catheter from the needle axis.
Accordingly, it is an object of the present invention to provide a catheter which does not require a stylet for the insertion operation.
Another object is to provide such a catheter which is economical to produce.
A further object is to provide a thread assist device (TAD) to facilitate passage of a catheter through a needle.
In one aspect, the present invention relates to a stylet-free catheter for insertion into a patient via a needle, wherein the needle defines proximally a needle hub and distally a needle tip. The catheter comprises a proximal end, a distal end, and a body connecting the proximal and distal ends. The body defines therealong a stiffening section of a predetermined length disposed a predetermined distance proximally of the distal end such that it is located generally about an area where the body approaches the needle hub when the distal end approaches the needle tip. The stiffening section has a flexural stiffness at least twice that of the remainder of the body.
In a preferred embodiment, the stiffening section has a length of about 5 (preferably 7) cm, disposed from about 10 cm to about 15 cm proximally of the distal end, and has a diameter not exceeding the diameter of the remainder of the body by more than about 0.15 mm.
In one preferred embodiment, the stiffening section is formed of plastic tubing and a cured adhesive extending circumferentially about the plastic tubing to provide a stiffening coating. The cured adhesive preferably is UV-cured in situ. In an alternatively preferred embodiment, the stiffening section is formed of plastic tubing and a plastic sleeve heat-shrunk about the plastic tubing to stiffen the plastic tubing. The sleeve is preferably polyethylene terephthalate (PET). In both preferred embodiments, the stiffening coating/sleeve is non-tacky and wear-resistant, has a thickness not exceeding about 0.08 mm, extends in a substantially uniform thickness along the stiffening section and about the plastic tubing, and reinforces the plastic tubing of the stiffening section.
The present invention also encompasses in combination such a catheter and a needle defining proximally a needle hub and distally a needle tip.
The present invention further encompasses a thread assist device to reduce buckling of a catheter being inserted through a needle. The TAD comprises a body defining a proximal end, a distal end substantially spaced along a longitudinal axis form the proximal end, and a sidewall connecting the proximal and distal ends. The TAD distal end is configured and dimensioned for at least partial receipt and releasable maintenance within a hub of a needle, and the TAD sidewall is configured and dimensioned to enable axial sliding manipulation of a catheter through the needle hub and through the needle by a user. The TAD proximal and distal ends substantially preclude non-axial or lateral movement of the catheter at the TAD ends, and the TAD sidewall limits non-axial or lateral movement of the catheter between the TAD ends. In a preferred embodiment, the TAD sidewall is generally cylindrical but extends no more than 180xc2x0 about the TAD body intermediate the TAD proximal and distal ends to define a gap intermediate its long edges such that a user can establish axial sliding manipulation of the catheter through the gap and further limit non-axial movement of the catheter between the TAD ends.
In another embodiment, the TAD sidewall extends over an arc of no more than about 90xc2x0 about the TAD body intermediate the TAD ends and is slightly bowed outwardly from the TAD longitudinal axis for substantially the entire length of the TAD sidewall along the catheter, thereby to increase the potential extent of contact between the user and the catheter between the TAD ends and thus facilitate grasping and generally axial movement of the catheter through the TAD by the user.
The present invention also encompasses in combination such thread assist device, a catheter, and a needle, the distal end of the TAD being at least partially disposed in the hub of the needle, and the catheter extending through the TAD proximal end, along the TAD sidewall, through the TAD distal end and into the needle.
Further, the present invention specifically encompasses the combination of such a catheter and such a TAD.